1. Field of the Invention
The present invention relates to a vane type compressor which is, in particular, used for compressing a refrigerant in an air conditioning system for an internal combustion engine.
2. Description of Related Art
Known in the prior art is a vane type multi-cylinder compressor of concentric rotor type, which has a cylinder of an elliptic cross sectional shape, in which a rotor of a pillar shape of a circular cross-section is arranged concentric, so that the rotor subjected to a rotational movement from an outside driving source is rotated while being contacted with an inner surface of the cylinder at its two locations. Also known in the prior art is a compressor of eccentric rotor type, which has a cylinder of a circular cross-sectional shape, in which a rotor of pillar shape of a circular cross-section is arranged eccentric, so that the rotor subjected to a rotational movement from an outside driving source is rotated while being contacted with an inner surface of the cylinder at its one location.
In both of the above compressors, a plurality of vanes are radially slidably inserted to the rotor, so that the vanes are urged by respective springs to contact with the inner surface of the cylinder, so that an operating chamber between the cylinder and the rotor is divided into a plurality of cylinder sections (working chambers). A number of sets of combinations of an inlet and an outlet port, corresponding to a half of the number of the cylinder sections, is provided. Namely, a pair of inlet and outlet ports is provided when the number of working cylinders is two, and, two pairs of inlet and outlet ports are provided when the number of the cylinder sections is four. During the rotating movement of the rotor while the vanes are radially reciprocated, the volume of the working chambers is varied, so that a working cycle is performed which consists of an admission period where an admission of a fluid medium is done from the inlet port to a working chamber of which the volume is increasing, a compression period where the fluid medium in the working chamber is subjected to a compression when the volume of the working chamber is decreasing, and a discharge period where the fluid compressed at the compression chamber is discharged via the outlet port.
In the compressor of the conventional type, a number of working cycles, corresponding to the number of the compression chambers, is done for every complete rotation of the rotor. Namely, four working cycles are done during one rotation when the number of the compression chambers is four. As a result, in the variation in the driving torque of the rotor, a component related to the number of working chambers (a component of the 4th order in case of 4 working chambers) becomes high. As a result, a resonance in the refrigerant recirculating pipe line is obtained at a low rotational speed area, causing a noise to be easily generated.
A reduction of the number of the cylinder sections (working cheers) allows the resonance area for the pipe line to be reduced. However, the reduction of the number of the working chambers causes the variation in the driving torque to become large, causing the vibration of the compressor to increase. The increase in the vibration of the compressor causes the operating noise to become large, which makes the users feel uncomfortable on one hand, and the service life of the compressor to be reduced on the other hand.